Method of producing liquid oxygen and/or liquid nitrogen



Nov. 2, 196a s. SHAIEVITZ ETAL METHOD OF PRODUCING LIQUID OXYGEN AND/OR LIQUID NITROGEN Filed April 15, 1965 N Essa -28 *IIIi a I k jiii: m w. I 5 I WWW N v QM W fi MAJ QEEEG M A l l u l P w= YH f mm mm .3 @525: MW. l h 0 amma 3am: H H mm c aw .!u! I 334; J 3 n W oanna Y Q was Q B x 626 J om WA a 3 g E 4 E2 x25 ias 2 was 2 2:38 :32: 2; 52 ea 52: AEQQEZ 2%: s3 :9: ESE; L 23: Ebm Q E vs m Q Q E565 mm SE W 3 55858 vw ow E26 \9 ETQ E 9 23: J 8 momfigsou $55.5. Mr

N- mokwwafim 15085; F QBEEMW United States Patent 3,214,926 IVIETHOD OF PRODUCING LIQUID OXYGEN AND/OR LIQUID NITROGEN Sidney Shaievitz, Yonkers, N.Y., and Joseph T. Bernstein, Westport, Conn.; said Shaievitz assignor to North mnerican Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Apr. 15, 1963, Ser. No. 273,638 6 Claims. (Cl. 62l4) This invention relates to an apparatus and method for producing liquid oxygen and/or liquid nitrogen.

An object of the present invention is to provide apparatus for producing liquid oxygen and/ or liquid nitrogen in which the maximum pressure of any stream in the apparatus is no greater than approximately 100 p.s.i.a.

Another object of the present invention is to provide an apparatus or plant having a minimum height dimensions resulting from the fact that the high pressure column is separated from the low pressure column. Furthermore, the aforesaid single columns operate satisfactorily without the use of mechanical pumps or vapor lift devices.

A further object of the present invention is to provide a plant for producing both liquid oxygen and liquid nitrogen in which all products are in a liquid state, and the plant includes self-cleansing reversing heat exchangers with respect to moisture and carbon dioxide entering the system.

Another object of the present invention is the provision of an apparatus for producing liquid oxygen and/ or liquid nitrogen that is reliably eifective for the purposes intended.

The above and other features, objects and advantages of the present invention will be fully understood from the following description considered in connection with the accompanying illustrative drawing.

The sole figure is a schematic flow sheet of the apparatus and method constructed in accordance with the teachings of the present invention.

Referring more particularly to the drawing in which liquid oxygen is produced as a product, atmospheric air is drawn into the suction of air compressor 12 through a filter 10. In compressor 12 the air is compressed to approximately 75 p.s.i.g. Thereafter the compressed air is passed through after-cooler 14 and water separator 16. By the proper positioning of the reversing valve 18, the compressed air is directed to one set of the reversing passages of the reversing heat exchanger 20. Although element 20 is herein illustrated as a reversing heat exchanger it is considered to be within the scope of the present invention to utilize a pair of regenerators (not shown) for the reversing heat exchanger 20 The air in flowing through one set of reversing passages in the heat exchanger 20 is cooled to within a few degrees of its dew point. In addition, the water and carbon dioxide content of the air are deposited on the cold surfaces of the heat exchanger 20 as the air is cooled. Waste nitrogen flows through the other set of reversing passages and serves to cool the incoming air. As a result of the small temperature difference between the waste nitrogen at atmospheric pressure and the air, the waste nitrogen is able to evaporate the carbon dioxide and moisture previously deposited by the air. The two reversing sets of passages in the reversing heat exchanger 20 are periodically switched over. Exiting from the reversing heat exchanger 20 the cold, purified air flows to the proper pipe as a result of the arrangement of check valves 23, 25, 27 and 29.

The present invention is unique in the manner in which the close temperature approaches are achieved in the reversing heat exchanger 20.

In a conventional low pressure plant a gaseous product, e.g., oxygen, is rewarmed in non-reversing passages of the ice reversing exchanger. In order to effect carbon dioxide cleanup in the reversing exchanger, a portion of the cold, moisture and carbon dioxide free air is partially rewarmed by passing it through non-reversing passages and withdrawing it at about the midpoint of the reversing exchanger. In another method a portion of the cooling air is withdrawn from the midpoint of the reversing exchanger. The remainder of the air is further cooled in the cold portion of the reversing exchanger wherein it deposits its carbon dioxide content which is later evaporated by waste nitrogen. The carbon dioxide content of the air withdrawn from the midpoint of the reversing exchanger is removed by conventional means such as low temperature adsorption, The above approaches, however, are not feasible in the present situation where only liquefied products are produced and no gaseous products, such as oxygen, are returned through the reversing heat exchanger.

One known system of operating reversing heat exchangers in a self-cleaning state when used in an allliquid-products plant is to recycle a portion of the cooled, purified air entirely through the heat exchanger so that it is rewarrned to essentially ambient temperature. This method will provide the close temperature approaches necessary for carbon dioxide and water cleanup. However, the area of the closest temperature approach occurs at the mid-point of the heat exchanger which is a place where close temperature approaches are unnecessary for carbon dioxide or water cleanup. For carbon dioxide cleanup, close temperature approaches are required in the cold end of the reversing heat exchanger. In regard to moisture cleanup, close temperatures approaches are necessary in the warmer portion of the reversing heat exchanger. In the colder portion of the reversing heat exchanger there is essentially no water remaining in the air stream, and therefore none to clean up. The method of Warming the recycle air to ambient temperature, although it solves the problem of close temperature approaches, results in small temperature differences where not necessary and hence results in an excessive heat transfer surface requirement.

In this invention the close temperature approaches for carbon dioxide and moisture cleanup are effected only where necessary and as a result heat transfer surface area requirements are minimized. As seen in the drawing, this is accomplished by recycling a portion of the cold, carbon dioxide and moisture-free air through the colder portion of the reversing heat exchanger. This is achieved by the setting of valves 21, 22 and 24. A fraction of this recycle stream is further recycled through the pipe 26 and the rest of the reversing heat exchanger and warmed to nearly ambient temperature. Both portions of the recycle stream are recombined with the main air stream 28 as illustrated in the drawing.

In order to avoid liquefaction of air in the reversing heat exchanger 20 with resultant excessive switch losses it is necessary to insure that the waste nitrogen entering the heat exchanger is at most only slightly below the dew point of the air stream and yet cold enough to cool the air to a sufficiently low temperature to effect carbon dioxide removal from the air in the reversing heat exchanger 20. This is accomplished in the lower half of the control heat exchanger 30. As seen in the drawing, the air stream is split by means of valves 32 and 34 in such a manner that the portion of the air flowing through valve 32 is sufficient to warm waste nitrogen to the required temperature. The two air streams are then recombined at 36.

The air stream continues to flow through the reboiler 38 of the high pressure column 40 wherein it is further cooled and supplies the reboil heat for the high pressure column. The high pressure air, still in a gaseous phase, passes through pipe 42 and through one of two hydro- 3. carbon adsorbers 44 (only one shown). are operated in a manner known in the art.

At the outlet of the adsorbers 44 the air is separated at a point 46 into two fractions by the proper settings of valves 48 and 50. That portion flowing through valve 48 forms the feed to the high pressure column 40. This stream is rectified in the high pressure column 40 in order to produce a gaseous nitrogen overhead and a crude liquid oxygen bottoms. The bottoms of the high pressure column 40 are throttled through valve 52 into the low pressure column 54. The low pressure column 54 is of a design well known in the art. The nitrogen overhead of the high pressure column 40 is liquefied by the refrigerator 56. preferably of the cold-gas refrigerator type. The liquid nitrogen collects in the reservoir 58 after which it is sub-cooled by waste nitrogen in the control heat exchanger 30 and is expanded through valve 60 to form the reflux necessary for operation of the low pressure column 54.

The other fraction of the air that was split downstream of the hydrocarbon adsorbers 44 flows to the reboiler 62 of the low pressure column 54 where it is liquefied and supplies the necessary reboil energy for operation of this column. This stream is then expanded through valve 50 into the condenser 64 of the high pressure column 40. In the condenser the low pressure liquid air evaporates by condensing a portion of the nitrogen gas issuing from the top tray of the high pressure column 40. The condensed nitrogen forms the reflux for the high pressure column. Valve 66 is used to control the liquid level of the air in the condenser 64. The air that is vaporized in the condenser 64 is recondensed by the refrigerator 57, preferably of the cold gas refrigerator type. The liquefied air is then fed to the appropriate tray of the low pressure column 54 through line 67.

The liquid oxygen is drawn from the bottom of the low pressure column 54 at 68, is subcooled by waste nitrogen in the control heat exchanger 30 and forms the liquid oxygen product 70. The waste nitrogen overhead of the low pressure column 54 is conducted away through pipe 72 and is cooled to ambient temperature by progressively flowing through the control heat exchanger 30 and the reversing heat exchanger 20.

If a liquid nitrogen product is desired either concurrently with the production of liquid oxygen or alone, this liquid nitrogen product is withdrawn through a valve 74 after being subcooled by waste nitrogen in the control heat exchanger 30 as illustrated in the drawing. The production of liquid nitrogen occurs at the expense of reflux for the low pressure column 54 and hence at the expense of liquid oxygen production. It should be noted that the change from liquid oxygen production will occur smoothly with a minimum upset of the plant streams.

While we have shown and described the preferred embodiment of our invention, it will be understood that the latter may be embodied otherwise than as herein specifically illustrated or described and that in the illustrated embodiment certain changes in the details of construction and in the arrangement of parts may be made without departing from the underlying idea or principle of the invention within the scope of the appended claims.

What we claim is:

1. A method of producing liquid oxygen and/ or liquid nitrogen comprising compressing atmospheric air to approximately 75 p.s.i.g., directing said air stream through a system of reverting valves into a reversing heat exchanger, said reversing heat exchanger having a waste nitrogen stream which serves to cool said incoming air to within a few degrees of its dew point and to evaporate the moisture and carbon dioxide previously deposited in the reversing heat exchangers by the incoming air, passing said air through a check valve arrangement and part of said air being recycled through approximately one half of said reversing heat exchanger and the remainder of said air being recycled through the entire heat exchanger,

The adsorbers said recycled air being joined together and part thereof passed through a control heat exchanger, conducting the combined air stream through a reboiler of high pressure column and directing part of the same as a feed for said high pressure column, rectifying said part of the air stream in said high pressure column to produce a gaseous nitrogen overhead and liquid oxygen bottoms, throttling the bottoms of said high pressure column through a valve and into a low pressure column, liquefying the gaseous nitrogen overhead of said high pressure column by means of a cold source to form the liquid nitrogen product and the reflux for said low pressure column, directing the other part of said air stream to the reboiler of said low pressure column, expanding said other part of said air stream through a valve to the condenser of said high pressure column, reliquefying said air and passing the product into the low pressure column, and withdrawing liquid oxygen from the bottom of said low pressure column.

2. A method of producing liquid oxygen and/ or liquid nitrogen comprising compressing atmospheric air to approximately 75 p.s.i.g., directing said air stream through a system of reversing valves into a reversing heat exchanger, said reversing heat exchanger having a waste nitrogen stream which serves to cool said incoming air to within a few degrees of its dew point and to evaporate the moisture and carbon dioxide previously deposited in the reversing heat exchangers by the incoming air, passing said air through a check valve arrangement and part of said air being recycled through approximately one half of said reversing heat exchanger and the remainder of said air being recycled through the entire heat exchanger, said recycled air being joined together and part thereof passed through a control heat exchanger, conducting the combined air stream through a reboiler of a high pressure column, passing said air stream through a hydrocarbon adsorber, separating said air stream into two parts at the outlet of said adsorber, and directing one part of said air stream as a feed for said high pressure column, rectifying said part of the air stream in said high pressure column to produce a gaseous nitrogen overhead and liquid oxygen bottoms, throttling the bottoms of said high pressure column through a valve and into a low pressure column, liquifying the gaseous nitrogen overhead of said high pressure column by means of a cold source to form the liquid nitrogen product and the reflux for said low pressure column, directing the other part of said air stream to the reboiler of said low pressure column, expanding said other part of said air stream through a valve to the condenser of said high pressure column, reliquefying said air and passing the product into the low pressure column, and withdrawing liquid oxygen from the bottom of said low pressure column.

3. A method of producing liquid oxygen and/ or liquid nitrogen comprising compressing atmospheric air to approximately 75 p.s.i.g., directing said air stream through a system of reversing valves into a reversing heat exchanger, said reversing heat exchanger having a waste nitrogen stream which serves to cool said incoming air to within a few degrees of its dew point and to evaporate the moisture and carbon dioxide previously deposited in the reversing heat exchangers by the incoming air, passing said air through a check valve arrangement and part of said air being recycled through approximately one half of said reversing heat exchanger and the remainder of said air being recycled through the entire heat exchanger, said recycled air being joined together and part thereof through a control heat exchanger, conducting the combined air stream through a reboiler of a high pressure column and directing part of the same as a feed for said high pressure column, rectifying said part of the air stream in said high pressure column to produce a gaseous nitrogen overhead and liquid oxygen bottoms, throttling the bottoms of said high pressure column through a valve and into a low pressure column, liquefying the gaseous nitrogen ove ead Of said high pressure column by means of a cold source, and subcooling said liquefied nitrogen by the waste nitrogen in said control heat exchanger to form the liquid nitrogen product and the reflux for said low pressure column, directing the other part of said air stream to the reboiler of said low pressure column, expanding said other part of said air stream through a valve to the condenser of said high pressure column, reliquefying said air and passing the product into the low pressure column, and withdrawing liquid oxygen from the bottom of said low pressure column.

4. A method of producing liquid oxygen and/ or liquid nitrogen comprising compressing atmospheric air to approximately 75 p.s.i.g., directing said air stream through a system of reversing valves into a reversing heat exchanger, said reversing heat exchanger having a waste nitrogen stream that is only slightly below the dew point of said air stream and which serves to cool said incoming air to within a few degrees of its dew point and to evaporate the moisture and carbon dioxide previously deposited in the reversing heat exchangers by the incoming air, passing said air through a check valve arrangement and part of said air being recycled through approximately one half of said reversing heat exchanger and the remainder of said air being recycled through the entire heat exchanger, said recycled air being joined together and part thereof passed through a control heat exchanger, conducting the combined air stream through a reboiler of a high pressure column and directing part of the same as a feed for said high pressure column, rectifying said part of the air stream in said high pressure column to produce a gaseous nitrogen overhead and liquid oxygen bottoms, throttling the bottoms of said high pressure column through a valve and into a low pressure column, liquefying the gaseous nitrogen overhead of said high pressure column by means of a cold gas refrigerator to form the liquid nitrogen product and expanding through a valve to form the reflux for said low pressure column, directing the other part of said air stream to the reboiler of said low pressure column, expanding said other part of said air stream through a valve to the condense-r of said high pressure column, reliquefying said air and passing the product into the low pressure column, and withdrawing liquid oxygen from the bottom of said low pressure column.

5. A method of producing liquid oxygen and/ or liquid nitrogen comprising compressing atmospheric air in a range of approximately 65 p.s.ig. to 100 p.s.i.g., directing said air stream through a system of reversing valves into a reversing heat exchanger, said reversing heat exchanger having a waste nitrogen stream which serves to cool said incoming air to within a few degrees of its dew point and to evaporate the moisture and carbon dioxide previously deposited in the reversing heat exchanger by the incoming air, passing said air through a valve arrangement and part of said air being recycled through approximately one half of said reversing heat exchanger and the remainder of said air part being recycled through the entire heat exchanger, said recycled air being joined together with the air not recycled, and passing part of said combined air stream through a control heat exchanger, recombining said part of said air stream which has passed through said control heat exchanger with the remainder of said air stream, conducting the combined air stream through a reboiler of a high pressure column and directing part of the same as a feed for said high pressure column, rectifying said part of the air stream in said high pressure column to produce a gaseous nitrogen overhead and crude liquid oxygen bottoms, throttling said bottoms of said high pressure column into a low pressure column, liquefying the gaseous nitrogen overhead of said high pressure column by means of a cold source to form the liquid nitrogen product and the reflux for said low pressure column, directing the other part of said air stream to the reboiler of said low pressure column, expanding said other part of said air stream into the condenser of said high pressure column, reliquefying said air coming from said condenser and passing said liquid air into the low pressure column, and withdrawing liquid oxygen from the bottom of said low pressure column.

6. A method of producing liquid oxygen and/ or liquid nitrogen as claimed in claim 5 wherein said liquid oxygen and said nitrogen reflux are subcooled in said control heat exchanger which, at the same time, warms up said waste nitrogen stream.

References Cited by the Examiner UNITED STATES PATENTS 1,449,291 3/23 Mewes.

1,594,336 7/26 Mewes 62-29 X 1,880,981 10/32 Pollitzer 62-29 X 2,650,481 9/53 Cooper 62-14 2,763,138 9/56 Tsunoda 62-13 2,824,433 2/58 Kohler 62-29 X 2,840,994 7/58 Lobo 6214 2,850,880 9/58 Jakob 62-13 X NORMAN YUDKOFF, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,214,926 November 2, 1965 Sidney Shaievitz et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 66, for "reverting" read reversing Signed and sealed this 9th day of August 1966.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner of Patents 

1. A METHOD OF PRODUCING LIQUID OXYGEN AND/OR LIQUID NITROGEN-COMPRISING COMPRESSING ATMOSPHERIC AIR TO APPROXIMATELY 75 P.S.I.G., DIRECTING SAID AIR STREAM THROUGH A SYSTEM OF REVERTING VALVES INTO A REVERSING HEAT EXCHANGER, SAID REVERSING HEAT EXCHANGER HAVING A WASTE NITROGEN STREAM WHICH SERVES TO COOL SAID INCOMING AIR TO WITHIN A FEW DEGREES OF ITS DEW POINT AND TO EVAPORATE THE MOISTURE AND CARBON DIOXIDE PREVIOUSLY DEPOSITED IN THE REVERSING HEAT EXCHANGERS BY THE INCOMING AIR, PASSING SAID AIR THROUGH A CHECK VALVE ARRANGMENT AND PART OF SAID AIR BEING RECYCLED THROUGH APPROXIMATELY ONE HALF OF SAID REVERSING HEAT EXCHANGER AND THE REMAINDER OF SAID AIR BEING RECYCLED THROUGH THE ENTIRE HEAT EXCHANGER, SAID RECYCLED AIR BEING JOINED TOGETHER AND PART THEREOF PASSED THROUGH A CONTROL HEAT EXCHANGER, CONDUCTING THE COMBINED AIR STREAM THROUGH A REBOILER OF HIGH PRESSURE COLUMN AND DIRECTING PART OF THE SAME AS A FEED FOR SAID HIGH PRESSURE COLUMN, RECTIFYING SAID PART OF THE AIR STREAM IN SAID HIGH PRESSURE COLUMN TO PRODUCE A GASEOUS NITROGEN OVERHEAD AND LIQUID OXYGEN BOTTOMS, THROTTLING THE BOTTOMS OF SAID HIGH PRESSURE COLUMN THROUGH A VALVE AND INTO A LOW PRESSURE COLUMN, LIQUEFYING THE GASEOUS NITROGEN OVERHEAD OF SAID HIGH PRESSURE COLUMN BY MEANS OF A COLD SOURCE TO FORM THE LIQUID NITROGEN PRODUCT AND THE REFLUX FOR SAID LOW PRESSURE COLUMN, DIRECTING THE OTHER PART OF SAID AIR STREAM TO THE REBOILER OF SAID LOW PRESSURE COLUMN, EXPANDING SAID OTHER PART OF SAID AIR STREAM THROUGH A VALVE TO THE CONDENSER OF SAID HIGH PRESSURE COLUMN, RELIQUELYING SAID AIR AND PASSING THE PRODUCT INTO THE LOW PRESSURE COLUMN, AND WITHDRAWING LIQUID OXYGEN FROM THE BOTTOM OF SAID LOW PRESSURE COLUMN. 